Alaska Science Forum

This article is provided as a public service by the Geophysical Institute, University of Alaska Fairbanks, in cooperation with the UAF research community. Guest author Joseph Niebauer is an Associate Professor of Marine Science.

Top two lines in chart depict mean high and low temperatures in interior Alaska through 1956, as taken from chart constructed by Dan Wilder. Bottom line depicts ice cover in the Bering Sea during 1973-1978. Note that fluctuations in temperature trends during periods in December through March are followed closely by corresponding changed in sea ice cover.

In an earlier column, a perspective on Alaska weather was presented which included a chart detailing the characteristics of weather patterns in central interior Alaska. The chart was drawn in 1956 by Dan Wilder and included, among other things, the record high, low and mean temperatures for each day of the year. It was noted that a primary feature of Dan Wilder's chart was a series of alternating temperature highs and lows in January, February and March.

In 1979, we calculated the mean ice cover for each week for the period 1973-1978 for the eastern Bering Sea, a large semi-enclosed sea to the west of mainland Alaska and north of the Aleutians. We then plotted a six-year mean and found, in addition to the strong seasonal cycle, alternating ice cover fluctuations from December through March. These fluctuations can best be characterized as two slight retreats in the ice cover occurring at the end of December to the beginning of January and from late February to the beginning of March. Notice that they coincide with the two periods of slight rises in the interior temperatures during the same time periods.

We think that these bumps in the graphs are caused by the same weather features which occur about the same time each year affecting both the interior Alaska air temperatures and Bering Sea ice cover. In the winter, strong low pressure systems, or storms, pass from west to east along the Aleutian Chain often coming off the Northern Pacific Ocean and Gulf of Alaska along the south and southeast coast of Alaska. This accounts for the heavy precipitation along the coasts. However, we found that nearly every year during the two periods mentioned above, one of these storms or low pressure systems would stall or stop in the Gulf of Alaska and then would actually back up or move toward the west back along the Aleutians and often into the Bering Sea. The air flow along the leading edge of this particular low is from south to north. Therefore as the storm backed up; it would send a flow of warm air northward over Alaska, raising temperatures in the Interior and causing ice in the Bering Sea to retreat. After about a week or so the storm track would be reestablished and the air temperature and ice cover would return to their normal patterns.